Seven monoclonal antibodies (MABs) against rat neurophysin have been produced and fully characterized. These MABS have been used in developmental studies in studies on the fetal rat hypothalamus. Differential expression of the specific properties of vasopressin- and oxytocin-neurons during development has been found. In addition, these MABs have been used to characterize the arginine vasotocin and mesotocin neurons in the Xenopus hypothalamus, where greater than 4000 neurons, which were found to contain these peptides, have been detected. Polyclonal antibodies have been generated against the various processing intermediates of vasopressin and oxytocin, as well as LHRH, and these are currently being used in RIA and immunocytochemical studies of the adult developing hypothalamus. Immunocytochemical studies have shown that vasopressin is coexistent with dynorphin in secretory vesicles in the neurohypophysis, and with CRF in the median eminence. The irregular (spinous dendrites) LHRH cells which develop during puberty, undergo this transformation independently of gonadal steroids. Ligand potency analyses of AVT (V2) receptors in the Xenopus A6 cell line and the toad bladder have shown that these amphibiansystems contain a novel V-2 receptor. A large repertoire of MABs have been produced against neuronal cytoskeletal proteins in the squid axon and the Xenopus nervous system. Analysis of the protein kinase-calcium activated protease-neurofilament complex in the squid giant axon has shown that the protein kinase is similar to type II casein kinase, but with a preference for histone substrates.